The present disclosure relates to heat shields, and more specifically, to heat shield materials.
A TPS is a barrier that protects a spacecraft from a variety of conditions. For example, a TPS may protect a spacecraft from searing heat experienced during atmospheric reentry. During orbit in space, a TPS also protects the spacecraft from large temperature variations (e.g., hot and cold). A variety of methods and devices are used for TPSs. For example, a TPS may use ablative heat shields and/or active and passible surface cooling devices.
An ablative heat shield functions as a TPS by lifting the hot shock layer gas away from the heat shield's exterior surface, which creates a cooler boundary layer. The heat shield repels gaseous reaction products away from its surface, which protects from heat flux. Establishing a boundary layer to reduce heat flux is called blockage.
A heat shield may be ablative in two respects. The outer surface of the heat shield material may char, melt, and sublime. The bulk material then may undergo pyrolysis and expel product gases. The expelled gas is driven away from the surface, and therefore, blocks heat flux, including convective heat flux, radiative heat flux, and catalytic heat flux.